The present invention is directed to methods of fabricating biobased materials and structures fabricated therewith, in particular to methods of fabricating printed wiring boards.
With the pervasive use of computers and work stations for personal and business applications, as well as the increasing level of intelligence being built into consumer appliances and automobiles, the volume of printed wiring boards, (PWBs) fabricated and assembled into such systems is likely to increase at a rapid rate for the foreseeable future. This trend, compounded by the short time span between successive generations of technological advances in these products and the associated obsolescence of older products, leads to a potentially significant problem of disposing of the PWBs in these products. The problem stems from the type of materials used in the manufacturing of the PWB composites. Traditionally, the PWBs are made of layers of thin sheets of thermosetting epoxy resins which are applied on to a woven fabric or a random dispersion of high modulus organic (carbon or aramid) or inorganic (glass) fibers. These laminates can be drilled, metallized and patterned to create vias and interconnection wiring. The individual layers are then laminated together and rigidified, or cured, by thermal and/or chemical means to achieve the final shape and desired electrical and mechanical characteristics, these composite laminates then become active circuit boards when electronic components are attached to them by lead containing solders. The amount of PWBs manufactured in this way is substantial: according to a 1989 report prepared by the Technology Marketing Research Council (T/MRC) of the IPC (Institute for Interconnection and Packaging of Electrical Circuits), PWB manufacturing activities worldwide consumed 1655 million square ft. of rigid laminate. The volume for North
American usage alone was 282 million square ft. The PWBs manufactured in 1989 will be obsolete eventually and will need to be disposed of as solid waste. The European Community has recently mandated a xe2x80x9ctake-backxe2x80x9d policy that forces acceptance of any and all returned items to the manufacturer specifically for recycling. Such regulations are likely to arise worldwide which will further exacerbate the laminate disposal problem and shift it to the manufacturing countries such as the U.S. Such PWB composites cannot be directly disposed in a landfill however, because of the space filling and non-degradable nature of their make up. Therefore, PWBs are generally ground up and incinerated first to reduce landfill volume. Some manufactures of PWBs voluntarily accept trade-ins of old equipment in exchange for new equipment purchases and incinerate the old PWBs. Although incineration is a form of recycling in that some energy is recovered, operation of incinerators with the appropriate scrubbers to ensure that emissions into the atmosphere are free of pollutants is expensive. Further, the process still generates 30% by weight of residual ash which in turn has to be handled, shipped and disposed of as toxic waste in a designated landfill, particularly because it contains metals like lead. The inorganic fibers used in PWBs are not toxic but they are not accessible to recycling in the composite form, thus contributing to the ash volume. An environmentally compatible solution to the problem, we believe, has to begin by focusing on seeking out reinforcing resinous materials, as well as interconnection and assembly materials that are by choice based on renewable resources, that are non-toxic and yet meet the performance demands of the electronic applications on hand. Further, it is desirable to seek options that, when possible, reduce or eliminate the use of environmentally unacceptable chemicals and solvents and consume less energy to manufacture thus providing cost and further ecological advantages.
It is an object of the present invention to substitute the resins and fibers currently used with bio-based materials. Bio-based materials are defined as materials derived from renewable resources by chemical or mechanical means or products derived from biological sources.
It is another object of the present invention to provide reinforced composites, and methods of fabrication thereof using biobased renewable resources for manufacture of printed wiring boards (PWB) that meet or exceed the thermal, mechanical and electrical performance requirements of FR-4 (epoxy based) grade laminates.
It is another object of the present invention to produce PWBs that are comparable in performance to those currently used and yet, at the end of their service life be amenable to waste treatment at least partially by biodegradability.
It is another object of the present invention to replace the petroleum based epoxies currently used in the manufacture of printed circuit cards (such as FR-4) with biobased materials.
A broad aspect of the present invention is a method of fabricating a cross-linked polymer selected from the group of lignin, crop oils, wood resins, tannins, polysaccharide resins and combinations thereof.
A more particular aspect of the present invention is a method of fabricating a printed circuit board from the cross-linked polymers according to the present invention.